A cord reel stores a length of wire in a convenient small housing unit until the wire is needed, at which time a user can pull out the length of wire required by the situation. When the user no longer needs the wire, a spring inside the cord reel retracts the length of wire back into the housing.
One conventional application of a cord reel is a mechanic's "drop light." Drop lights were often found in auto repair shops hanging from the ceiling just above head height. When a light was needed, a mechanic would grab the drop light and pull the desired amount of electrical cord from the cord reel (attached to the shop ceiling). When the mechanic no longer need the light, the cord reel would retract the cord. This eliminated the need for many loose wires and extension cords lying on the shop floor which could get tangled or damaged.
The earlier developed cord reels were typically limited to electrical power applications since they relied on electrical brushes and slip rings to achieve electrical continuity between the stationary cord reel housing and rotating cord reel spool. Brushes typically cause short interruptions in continuity due to their sliding nature, which does not usually affect most simple electrical devices as lights and motors,-but have a severe detrimental effect on precise equipment such as communication devices. In analog devices, these interruptions appear as noise or static. In digital devices, these interruptions will cause loss of bits of information, which could at times cause data transmission to be incomplete or lost, or worse yet, incorrect.
It was not until the development of the brushless cord reels (e.g., reels which do not use brushes and slip rings) that cord reels became widely used for communication purposes. Instead of brushes, these cord reels have a "stationary" cord bridging the spool and housing, providing uninterrupted, continuous contact throughout cord reel operation. While the usable portion of the cord is extended and retracted, the stationary cord is allowed to coil and uncoil between the rotating spool and stationary housing.